Dry eye is a disorder of the tear film due to tear deficiency or excessive tear evaporation which causes damage to the interpalpebral ocular surface associated with symptoms of ocular discomfort (Smith, The Ocular Surface 5(2): 93-407 (2007)). Chronic dryness leads to pain and irritation that is often debilitating to the subject, preventing the performance of normal daily activities such as reading, driving, among other things. Dry eye is increasing in prevalence as population ages. Approximately 4.9 million Americans 50 years and older have dry eye, and many more have less severe symptoms notable only during contact with adverse contributing factors such as low humidity or contact lens wear (Smith, 2007), as well as the 21 million individuals with diabetes. The number of women affected with dry eye appears to exceed that of men.
Currently dry eye includes two major classes: aqueous tear-deficient dry eye (ADDE) and evaporative dry eye (EDE). ADDE mainly refers to a failure of reflex lacrimal secretion, but also includes a failure of non-reflex water secretion by the conjunctiva. ADDE has two major subclasses, Sjogren Syndrome dry eye (SSDE) and non-SS dry eye. EDE may be intrinsic, where dry eye is due to intrinsic disease affecting lid structures or dynamics, or extrinsic, where ocular surface disease occurs due to some extrinsic exposure such as topical drug preservatives, contact lens wear or vitamin A deficiency. See review by Lemp, The Ocular Surface 5(2): 75-92 (2007).
Substantiated risk factors for developing dry eye include female sex, older age, postmenopausal estrogen therapy, diabetes mellitus, a diet that is low in omega 3 essential fatty acids or has a high ratio of omega 6 to omega 3 fatty acids, refractive surgery, vitamin A deficiency, radiation therapy, bone marrow transplant, hepatitis C, certain classes of systemic and ocular medications including anti-histamines (Smith, 2007). Other risk factors may include HIV, human T cell lymphotropic virus-1 infection, connective tissue diseases, systemic cancer chemotherapy, and certain other medications (Smith, 2007).
Current therapies for dry eye include tear supplementation (e.g., lubricants), tear retention, tear stimulation, tear substitutes, anti-inflammatory therapy, and essentially fatty acids, as discussed in a review article (Pflugfelder, The Ocular Surface 5(2): 163-178, 2007). Over-the-counter lubricants are most frequently prescribed by vision specialists; however lubricants offer only temporary relief, can be expensive, and need to be taken for life. The cause of dry eye is not treated with lubricants.